Many of the existing hydrocarbon formations have been produced to such a point that the natural gas available in these reserves is at low pressures or below atmospheric pressure. To produce natural gas from these reserves, the gas must be pumped from the formation and compressed for sale. The cost to pump and compress gas can be substantial; therefore, cost saving measures are important in making retrieval of the gas economically viable.
Generally a self contained compression system is used to extract natural gas from low or below pressure reserves, and is located on the well site. The compression system comprises a variety of apparatus, including a compressor. Typically, prior art compression systems employ a screw type compressor to draw gas from the formation and compress it for sale. However, screw compressors are expensive and require relatively high energy inputs to compress the gas. Further, these compressors have parts with metal-to-metal contact which require a constant oil source. The oil is deposited into the pump and eventually is carried away by the compressed gas, thus the screw pumps use oil and the oil source must regularly be replenished. Other compressor types commonly used in these applications also require a constant oil feed.
The gas extracted from some low or below pressure formations contain vapors and entrained liquid. Typical compression systems used with these wells must dry the gas before it can be compressed, because screw and other typical compressors cannot handle the liquid. In these systems, when the compressor encounters liquid or vapor the compressor will overload and shut down.
Therefore, there exists a need for a compression system which can handle gas having vapors and entrained liquid. Also, a closed oil system is desirable because the oil reserves need not be refilled as often. Finally, the compressor system should compress efficiently and at low cost.